Advanced oxidation processes, based on hydroxyl radical chemistry, can be used to successfully destroy chemical contaminants in waters intended for reuse. In determining the effectiveness of these radical oxidative degradations and transformations in water, both reaction rate constants and compound removal efficiencies must be considered. Removal efficiencies are defined as the number of contaminant molecules transformed per 100 hydroxyl radicals reacting. Hydroxyl radical reaction efficiencies have been determined for bisphenol A, caffeine, DEET, and sulfamethazine in different qualities of treated and model laboratory wastewaters. While these four contaminants show similar hydroxyl radical reaction rate constants, their removal efficiencies in deionized water varied significantly at 76±7, 92±8, 95±9, and 56±7%, respectively. Model wastewater studies showed that dissolved oxygen did not appreciably influence these values, and low levels of dissolved organic matter (DOM) reduced the removal efficiencies by an average of approximately 20%. However, the combination of solution alkalinity and DOM had a significant impact in reducing hydroxyl radical reaction efficiencies, although not always in a linear, additive, fashion. These results imply that the effective implementation of advanced oxidation technologies in wastewater treatments might be enhanced by prior removal of organics or alkalinity.